[SOLVED] Grub: root= device keeps switching sda to sdb

elmar283 · Last edited by elmar283 on Sun Aug 12, 2018 3:07 pm; edited 2 times in total

I have a Macbook Pro with MacOS and Gentoo on it.
I have two problems right now:
1. since a month when I boot sometimes the first harddrive (I have only one) is sda and sometimes it is sdb.
On /etc/fstab I solved this by replaceing the devicenames by UUID.
2. os-prober does not work.

The first queation I will ask here.

To fix the problem I have set the kernel "CONFIG_CMDLINE="root=PARTUUID=fc80794a-f214-41c3-a046-46403a8e4a63".

But 'grub-mkconfig' keeps passing on 'root=/dev/sda' in '/boot/grub/grub.cfg'.

I have three questions:
1. Why does hda keeps switching to hdb and back?
2. How can I stop 'grub-mkconfig' from passing the 'root=/dev/sda' in '/boot/grub/grub.cfg' or
3 Is it possible to set the UUID in '/etc/default/grub'?

I tried the last by setting 'GRUB_DEVICE="UUID=da72d0b5-bd89-4cb8-8958-c820691077d7"', but that doesn't work.

Some information about my system:
http://www.elmarotter.eu/bestanden/boxmodel/index.php?dir=Gentoo/grub

EDIT: I changed hda and hda to sda and sdb.

LIsLinuxIsSogood · Veteran Joined: 13 Feb 2016 Posts: 1179

NeddySeagoon · Posted: Sun Aug 05, 2018 12:32 pm Post subject:

elmar283,

To build on what LIsLinuxIsSogood is saying, please pastebin your dmesg output when your hdd is /dev/sdb.
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Jaglover · Posted: Sun Aug 05, 2018 12:49 pm Post subject:

There is SATA controller and AHCI in kernel. Why we are talking about hda/hdb? Why are those PATA drivers enabled in kernel?
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elmar283 · Posted: Sun Aug 05, 2018 1:56 pm Post subject:

elmar283 · Posted: Sun Aug 05, 2018 2:06 pm Post subject:

Here is the dmesg when system is sdb:
http://www.elmarotter.eu/bestanden/boxmodel/Gentoo/grub/dmesg_sdb.txt

Anon-E-moose · Posted: Sun Aug 05, 2018 2:07 pm Post subject:

Almost sounds like you have some external device plugged in (sometimes) which makes it change from sda to sdb.
Do you have any usb devices (disk, stick) ever plugged in before booting?
(I've had the bios interpret some usb sticks as hard disks)

edit to add: just looked at your last post

Jaglover · Posted: Sun Aug 05, 2018 2:10 pm Post subject:

elmar283 · Posted: Sun Aug 05, 2018 2:12 pm Post subject:

It seems to be a card reeder that is now sda:

Anon-E-moose · Posted: Sun Aug 05, 2018 2:20 pm Post subject:

LIsLinuxIsSogood · Veteran Joined: 13 Feb 2016 Posts: 1179

Anon-E-moose...I wonder if you by creating kernel modules there what would happen if there was a need for access to the files on those other storage devices early on like during the boot process still, and wouldn't this make a problem if that were the case?

Elmar, because I think we only answered the first of your questions here's answers to more of them.

LIsLinuxIsSogood · Veteran Joined: 13 Feb 2016 Posts: 1179

Here are some other things to be aware of :
Potential risks such as security risk that could be an unwanted boot entry in the configuration file, or maybe something that tries to boot up another network resouces or PXE from a network host, or operating system that you did not intend to have on there.

Not getting locked out of the system, meaning have a readily available way back in via a rescue system, or be sure to thoroughly inspect the grub file before rebooting to make sure what you are committing to it. I think grub does come with a way of testing this from within the operating system. Or you can just fire up a text editor always.

Don't count on there being an easy way to retrieve any of your difficult or hard efforts in configuration boot parameters and therefore make a backup of the configuration files you work with just like you would with a working kernel it makes sense (in my opinion) to have a grub.cfg.old in case of restoring or if the actual grub.cfg file becomes corrupt in which case it is likely that something could be wrong with grub itself and then what is easier, if grub is still correctly installed on the device then having a working kernel and grub boot file saves time here.

Lastly instead of relying on mkconfig to get it right, you can work with the grub.cfg file and the grub-mkconfig tool as either a last resort or to replace a missing boot configuration. But otherwise perhaps going into the file and seeing why it doesn't work...that sounds like a better idea.

So did you get root=/dev/sda to be working correctly, or are you still thinking to change it to root=UUID=

LIsLinuxIsSogood · Veteran Joined: 13 Feb 2016 Posts: 1179

And lastly see here: https://unix.stackexchange.com/questions/93767/why-cant-i-specify-my-root-fs-with-a-uuid

root=UUID only works with an initramfs, which if you don't have means you should be using root=PARTUUID instead.

elmar283 · Posted: Sun Aug 12, 2018 3:07 pm Post subject:

I sovled it by using Refind instead of grub. Now I can boot Gentoo and MacOS from refind.
I have put the partuid of /dev/sda4 in the kernel.

LIsLinuxIsSogood · Veteran Joined: 13 Feb 2016 Posts: 1179

I just got through making the change myself on my system...it only runs linux on it actually only Gentoo linux, but the funny thing is adding disks via SATA or USB or whatever could st ill have thrown in a wrench in the boot process.

So now I too can claim that I have a more reliable avenue to boot with the instruction embedded into the kernel itself (way to figure that out with little or no help elmar283) And Thanks by the way